In capsaicinoid molecules an aromatic ring is attached, generally through an amide functional group, to an aliphatic long chain. These molecules exist as solids. Because the solid physical state is not optimum for effective penetration into the skin, dermal formulations of capsaicinoids are either liquids, gels, or patches, whereby capsaicinoids have been solubilized and the resulting solution accordingly adapted to the nature of the dosage form. In dermal dosage forms, penetration enhancers are generally used to facilitate/enhance penetration of a capsaicinoid into the skin. The presence of an aliphatic chain in capsaicinoid molecules gives them an intrinsic ability to penetrate tissues such as skin or mucous membranes. However, the intrinsic ability of capsaicinoids to penetrate into the skin is impeded by the lack of thermodynamic activity when in solid form. A change of state from solid to liquid greatly enhances thermodynamic activity. Also, some of the formulation ingredients such as adhesives impede capsaicinoids' ability to diffuse out of the formulation and hence penetrate into the skin. This invention eliminates the necessity to include such ingredients (e.g., penetration enhancers or adhesives) and utilizes the intrinsic ability of capsaicinoids to penetrate skin much more effectively when compared to their solid state.
With the addition of every single ingredient to any formulation the level of concern rises with respect to physicochemical, pharmacological, and toxicological properties of the formulation. These concerns promote an inclination to keep the system as simple as possible. However, this high level of simplicity is not always attainable due to necessity to meet other performance requirements. Formulation of a capsaicinoid oil would eliminate the necessity to use penetration enhancers as it allows reliance on the intrinsic property of the capsaicinoid to penetrate the skin by simply changing its physical state.
Accordingly, it would be desirable to have new pharmaceutical dosage forms for the treatment of pain that include oils of capsaicinoids.